The present invention relates to data storage media libraries, and more particularly, to scalable digital data storage media libraries.
Digital data storage devices are utilized for storing information for use by data processing systems including computer systems. One commonly used data storage medium is tape storage, used in tape libraries, well suited for backup operations as well as for providing archival and retrieval operations for vast quantities of information content. In this regard, optical storage is also known for voluminous content storage and retrieval.
Tape libraries are known in the art. One example of a tape library is provided by the Ostwald U.S. Pat. No. 5,236,296. In that patent, a tape library is described in FIG. 8 as comprising a vast, semi-cylindrical array of tape cartridge storage slots aligned generally along a fixed radius of curvature. A central cartridge inventory is maintained by a library controller, so that logical requests for a particular drive and cartridge may be translated by the library controller into physical device locations and electromechanical operations. In this prior example, a media loader includes a robotic arm rotating at a focus of the cylindrical segment that is elevated and rotated to a particular cartridge storage slot. A picker-gripper mechanism of the arm then xe2x80x9cpicksxe2x80x9d and xe2x80x9cgripsxe2x80x9d the cartridge stored in the slot and moves the cartridge out of the slot and into a temporary transport slot of the arm. The robotic arm is then commanded to perform a second rotation/elevation operation in order to present the retrieved tape cartridge to a loading tray of the selected tape drive, and the drive then loads the cartridge and threads the tape for recording/playback operations, following initial setup and calibration routines conventional with tape drives. The drive may be one of several drives accessible by the robotic arm.
Typically, media loaders (e.g., tape cartridge loader) operate in accordance with a standardized command structure. One such command structure is found in the Small Computer System Interface-2 draft standard X3T9.2 Project 375D (ANSI X3.131-199X). In this particular industry specification, a medium changer device includes a medium transport element, at least one storage element, and a data transfer element. An import/export element may also be supported. A storage element is identified as a storage slot for storing a standard medium unit, such as a disk or a tape cartridge. In order to access data on a standard medium unit, a host system issues commands to both the medium loader and to the drive.
The commands to the loader may include xe2x80x9cmove mediumxe2x80x9d; or, xe2x80x9cexchange mediumxe2x80x9d and xe2x80x9cread element statusxe2x80x9d. Commands directed by the host to the drive may include xe2x80x9ctest unit readyxe2x80x9d, xe2x80x9cinquiryxe2x80x9d, xe2x80x9cstart-stopxe2x80x9d and xe2x80x9cload-unloadxe2x80x9d commands, in addition to the obvious xe2x80x9cread/writexe2x80x9d commands. One important characteristic about this command structure is that the logical address of the drive is supplied to the media loader as a destination, as well as to the drive itself for subsequent read or write operations from or to the selected and automatically loaded medium unit.
Individually, the data throughput rates of typical open systems tape drives range between 5 and 15 megabytes per second, and these throughput rates are increasing with new versions of tape drives. This data rate must be effectively doubled internally by a data route or bridge between the tape drives and the host system, which must simultaneously receive data from the host system and send data to the target tape drives. At a tape library system level, such throughput requirements must then be multiplied by the number of tape drives in the library to represent the aggregate data rate for the library system. This places internal throughput requirements on tape libraries at over e.g. 320 Bytes/second.
Further, advanced data transfer functionality in libraries can double the aggregate throughput requirements. And, future generations of tape drives will require two to four times the current bandwidth of individual tape drives. As such, current and future libraries have high internal aggregate bandwidth requirements (e.g. over a gigabyte/second) at the system level for data transfer between the tape drives in the library and host computers.
In conventional libraries, several tape drives are connected to a high bandwidth bridge for data transfer between the tape drives and the host computers. Such libraries have several shortcomings. For example, high bandwidth bridges capable of handling aggregate data transfer between several tape drives and host computers are required. Such high bandwidth bridges are complex and expensive. As the number of tape drives per bridge increases, and as the tape drive data transfer rates increase, more complex and expensive bridges with higher bandwidth are required to replace existing bridges. This has led to low reusability between library families, low fault tolerance because a bridge failure effectively renders all the tape drives connected to the bridge unusable, and rapid obsolescence with the introduction of later generations of tape drives with higher throughput. Further, due to the extreme data rates necessary in such conventional libraries, very expensive electronics and processors are utilized to perform generalized data processing in the library. As a result, due to high throughout demands, typically bridge devices in conventional libraries perform minimal or no data processing.
Conventional library Fibre Channel and bridge implementations are either one Fiber Channel interface to several SCSI bus interfaces, or several Fibre Channel interfaces to several SCSI bus interfaces in configuration. Also, conventional libraries are limited in their protocol conversions to encapsulation/de-encapsulation, such as encapsulating SCSI protocol within Fibre Channel Protocol. Although there may be several bridges present in such libraries, each bridge services several tape drives. Because most libraries allow incremental single tape drive additions, the design of the bridges dictates that the natural increment for bridges is not the same as that for tape drives (for example, if each bridge services 8 tape drives, a library system containing 10 tape drives must have two bridges, and the bridging capacity for 6 tape drives is wasted).
There is, therefore, a need for a data storage unit such a media library which provides high data throughput capability, and reliable and fail safe architecture, for overcoming significant limitations and drawbacks associated with the conventional media libraries.
The present invention alleviates the aforementioned shortcomings of conventional libraries. In one embodiment the present invention provides a digital data storage unit, such as tape library, comprising a multiplicity of storage media slots, each storage media slot for receiving a storage media unit, a plurality of storage media units loaded in particular ones of the storage media slots, a plurality of data transfer devices for writing data to and reading data from the storage media units, a plurality of data transfer device interfaces corresponding to the plurality of the data transfer devices, each data transfer device interface configured for transferring data between a corresponding data transfer device and a host computing environment, a loader mechanism for selectively moving a storage media unit between a storage media slot and one of the plurality of data storage drives, and a storage unit controller connected to the loader mechanism and to the data transfer device interfaces, wherein the storage unit controller is configured for connection to the host computing environment to receive and decode one or more host commands sent by the host computing environment at the storage unit controller, and for controlling the loader mechanism for selectively moving storage media units from the storage media slot locations to the data transfer devices for data transfer in response to host commands.
A digital data storage unit according to the present invention alleviates prior art shortcomings in handling the aggregate throughput rates of large libraries with respect to data routing and protocol conversion. As such, in one version, inexpensive/commodity components can be used for the data transfer device interfaces in a library system according to the present invention, because each data transfer device interface addresses only the bandwidth requirements of a single data transfer device. This approach allows the same data transfer device interface to be used by any data storage library, because the data transfer device interface can be embedded in a data transfer device canister. Further, a high level of redundancy is achieved wherein failure of a single data transfer device interface only affects a minimum number of data transfer devices. And, each data transfer device interface has excess processing bandwidth to accommodate higher data transfer requirements such for data mirroring and group parity such as tape parity groups.
By applying the principals of the present invention including distributed processing to the tasks of data routing and protocol conversion, a highly scalable digital data storage unit is provided using commodity parts while achieving high degrees of redundancy and fault tolerance. In one version, tape library system, and method of operating the same, according to the present invention provide a single data routing and protocol conversion solution that scales linearly with the number of tape drives in the library system, capable of handling the bandwidth requirements of high data rate tape devices. The present invention is useful for data storage libraries including tape drives, magnetic disk drives, optical disk drives or other storage devices.